These teachings relate generally to terahertz integrated circuits using carbon nanotube sources.
Terahertz radiation (frequencies from 300 GHz to 10 THz; wavelengths 1 mm to 30 μm; note that 1 THz=1,000 GHz)) has primary potential applications to security imaging, molecular and liquid spectroscopy and bio-medical imaging. Terahertz spectroscopy and imaging systems require a terahertz source and a terahertz detector, and several versions of such sources and detectors exist, some of which have been commercialized: 1) Quantum cascade lasers, used by Kim et al. and Lee et al. while compact and capable of producing multi-mW powers, are limited to operating at cryogenic temperatures and produce radiation patterns that are difficult to control. 2) Sources of the TDS type (“Time-Dependent Spectroscopy”) used for medical imaging by e.g. Fitzgerald et al. and Photomixers used for the type of same type of applications by e.g. Brown et al. operate at 300 K and have average output powers less than or about equal to 1 μW but require visible/Near Infra Red lasers that are neither compact nor inexpensive (Teraview, Inc.; >100 k$). 3) Schottky barrier diode multiplier sources (Commercially available; Virginia Diodes) can deliver 10's of μW to 100's of μW of power between 1 and 2 THz (up to several mW just below 1 THz) and are more compact but require special diode and circuit fabrication steps that lead to a price range in the several tens of k$. They also rely on the availability of a high power source at millimeter waves which adds to the cost. 4) Sources based on plasma effects in FET/HEMT channels produce broadband radiation with output powers ˜1 μW. Their fabrication requires complex processing to reach that power level. THz gas lasers are well-known THz sources with output power up to over 100 mW (Coherent DEOS). Gas lasers are very large (order of meters) and commercial versions sell for in excess of $300 k.
At microwave frequencies (up to 200 GHz at present) both sources and detectors (usually transistors), as well as other devices, are typically fabricated as monolithically integrated circuits (MMICs) on a single chip. These can be mass-produced and wireless technology makes heavy use of such MMICs, for example. Very little work has been performed on analogous integrated circuits for the THz range (Terahertz Integrated Circuits, TICs), especially above 1 THz. Microstrip lines were previously used for materials spectroscopy of very small amounts of lactose and biomolecules in water solution with Terahertz Time-Domain Spectroscopy (TDS), but TDS requires expensive short-pulse lasers and the overall TDS system is much less compact than our system. Terahertz detector technology has recently demonstrated detector arrays for THz imaging that are fabricated in inexpensive silicon MOS technology, so far up to 1 THz. The sources employed in these imaging systems are still not feasible to fabricate in any inexpensive technology.
There is a need for easy to fabricate terahertz integrated circuits that can be used in the above and similar applications.